Carbon-fiber reinforced plastics (CRFP) and glass-fiber reinforced plastics (GFRP) that use carbon fibers, glass fibers, or aramid fibers as reinforcing fibers have light weight and high durability. Therefore, these plastics are materials that are ideal for various constituent members that constitute automobiles, aircrafts, ships, and building components.
As a method of molding these fiber reinforced plastics (FRP), there is an autoclave molding method for pressurizing and/or heating and curing a laminate prepared by stacking prepreg sheets made of reinforcing fibers and an epoxy resin having high toughness in an autoclave (a pressure vessel), for example. A resin transfer molding (hereinafter referred to as “RTM”) method and a vacuum RTM method are also well known. The RTM method and the vacuum RTM is a method of molding a compound material by impregnating a matrix resin in a reinforcing fiber, by arranging in a mold a laminate (may also be called a preform) prepared by stacking plural dry reinforcing fiber sheets not impregnated with a matrix resin, and by injecting a low viscosity liquid matrix resin into the mold.
In producing a beam member by combining a reinforcing fiber base material prepared by combining various reinforcing fiber sheets, a gap occurs between reinforcing fiber base materials that form a pair (at a branching point of two reinforcing fiber base materials having a bent portion). The gap occurs because the reinforcing fiber base materials cannot be completely deformed at a right angle due to high rigidity of the fibers when the reinforcing fiber base materials are bent.
For example, in the case of producing a beam member having a T-shaped cross-sectional surface by the RTM method or the vacuum RTM method, two L-shaped reinforcing fiber base materials 10a, 10b and one flat-plate-shaped reinforcing fiber base material 10c are combined together to form a preform 11 of a T-shaped beam member for a production reason, as shown in FIG. 1. At this time, a wedge gap 12 is formed at a branching point (a portion corresponding to the bent portion of the L-shape reinforcing fiber base material) of the two L-shaped members and the flat-plate-shaped member joined together. When a resin is injected into the preform of the T-shaped beam member in a state that the wedge gap is left as it is, a molded article having a resin-rich gap is obtained. When this molded article is applied to a wing or the like of an aircraft, the resin-rich gap generates insufficient rigidity and insufficient junction strength when a large tensile load acts, and this has a possibility of becoming a start point of break. Because fibers of the branching point are disturbed by a resin injection pressure at a molding time and because a gap ratio of the preform locally varies, there is a risk of occurrence of a void which becomes an internal defect of the molded article in the resin-rich gap.
To avoid a defect and strength reduction during such a molding process, the gap portion needs to be reinforced beforehand at a stage of producing the preform. As a reinforcement measure, a method of molding where a preshaped rod object (a shaped filler) made of a fiber structure is filled into the gap is well known. For example, there is proposed an invention concerning a preshaped rod object (a shaped filler) which is prepared by integrating a core member having a wedge cross-sectional surface made of a string composite having two or more continuous string composites converged, and an external member made of a continuous string configured in a cylindrical shape that covers an external peripheral surface of the core member in close contact with the external peripheral surface; and a method of producing such a rod preshaped object (Patent Document 1).
This method has no problem when the method is applied to a beam member that has a uniform thickness, a constant cross-sectional shape, and a constant wedge gap in a longitudinal direction. However, when a beam member is used as a cantilever, for example, a beam member of which a thickness changes in a longitudinal direction (a thickness is reduced toward a front end portion) is sometimes required. In this case, a problem occurs because a cross-sectional surface of the gap changes continuously or at stages following a change of the thickness of the beam member. This is because the cross-sectional surface area of a shaped filler that fills the wedge gap is difficult to be changed along a longitudinal direction. When a shaped filler having a constant cross-sectional surface area is used, many gaps remain in some places, or conversely, a density of reinforcing fibers contained in the cross-sectional surface of the gap becomes excessive. As a result, strength reduction or delamination occurs easily.
As a means for solving the above problem, there is proposed an invention concerning a process and an apparatus for producing a preshaped rod object (a shaped filler) that can be applied to gap portions of various cross-sectional surfaces and shapes, by gradually taking out a split mold while pulling a base material to a longitudinal direction with a die of a split-mold structure, following preparation, in advance, of the base material of a cut pattern which takes into account a change of the cross-sectional surface of the shaped filler (Patent Document 2).
However, according to this invention, particularly in the case of producing a preform of a long beam member in which a cross-sectional surface of a gap changes continuously at plural times, many dies (split molds) need to be prepared to change the cross-sectional surface of the shaped filler. Therefore, facility cost to produce the shaped filler increases, and a work process becomes extremely complex. Further, when preforms of plural kinds of beam members are manufactured, a shaped filler that matches respective gaps of the preforms needs to be produced. Because dies need to be prepared or exchanged each time, it takes time and labor, resulting in inefficiency.